This invention relates to a detector utilizing the total reflection characteristic of light in an U-shaped bar to detect presence of an object which may be liquid, vapor and the like.
The conventional optical sensor, as shown in the Japanese patent publication 12-1225, comprises a U-shaped transparent bar with the bent portions disposed at a preset level of liquid in a container, a lamp at one end of the U-shaped bar and an inspecting portion at the other end. At the inspecting portion, one has to determine with his eyes the presence or absence of the liquid by observing change in the brightness thereon. Consequently, it is impossible to detect the liquid level remote from the liquid container. The conventional detector is formed with 45.degree. cut surfaces at both bent portions to ensure that light does not leak into the inspecting portion at the other end when it is immersed in the liquid.